using System;

namespace Narwhunderful.Aphelia.Framework.Security.Cryptography
{

    public abstract class MD5 : HashAlgorithm
    {

        uint[] _state = new uint[4];
        uint[] _count = new uint[2];
        byte[] _buffer = new byte[64];

        static private byte[] _padding = new byte[] {0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};

        // basic MD5 functions.
        static private uint F(uint x, uint y, uint z)
        {
            return (((x) & (y)) | ((~x) & (z)));
        }
        static private uint G(uint x, uint y, uint z)
        {
            return (((x) & (z)) | ((y) & (~z)));
        }
        static private uint H(uint x, uint y, uint z)
        {
            return ((x) ^ (y) ^ (z));
        }
        static private uint I(uint x, uint y, uint z)
        {
            return ((y) ^ ((x) | (~z)));
        }

        // rotates x left n bits.
        static private uint RotateLeft(uint x, byte n)
        {
            return (((x) << (n)) | ((x) >> (32 - (n))));
        }

        // FF, GG, HH, and II transformations for rounds 1, 2, 3, and 4. Rotation is separate from addition to prevent recomputation.
        static private void FF(ref uint a, uint b, uint c, uint d, uint x, byte s, uint ac)
        {
            (a) += F((b), (c), (d)) + (x) + (uint)(ac);
            (a) = RotateLeft((a), (s));
            (a) += (b);
        }
        static private void GG(ref uint a, uint b, uint c, uint d, uint x, byte s, uint ac)
        {
            (a) += G((b), (c), (d)) + (x) + (uint)(ac);
            (a) = RotateLeft((a), (s));
            (a) += (b);
        }
        static private void HH(ref uint a, uint b, uint c, uint d, uint x, byte s, uint ac)
        {
            (a) += H((b), (c), (d)) + (x) + (uint)(ac);
            (a) = RotateLeft((a), (s));
            (a) += (b);
        }
        static private void II(ref uint a, uint b, uint c, uint d, uint x, byte s, uint ac)
        {
            (a) += I((b), (c), (d)) + (x) + (uint)(ac);
            (a) = RotateLeft((a), (s));
            (a) += (b);
        }

        public MD5()
        {
            Initialize();
        }

        // MD5 initialization. Begins an MD5 operation, writing a new context.
        public override void Initialize()
        {
            _count[0] = _count[1] = 0;

            // Load magic initialization constants.
            _state[0] = 0x67452301;
            _state[1] = 0xefcdab89;
            _state[2] = 0x98badcfe;
            _state[3] = 0x10325476;
        }

        // MD5 block update operation. Continues an MD5 message-digest operation, processing another message block, and updating the context.
        protected override void HashCore(byte[] input, int offset, int count)
        {
            int i;
            int index;
            int partLen;

            // Compute number of bytes mod 64
            index = (int)((this._count[0] >> 3) & 0x3F);

            // Update number of bits
            if ((this._count[0] += (uint)((uint)count << 3)) < ((uint)count << 3))
                this._count[1]++;
            this._count[1] += ((uint)count >> 29);

            partLen = 64 - index;

            // Transform as many times as possible.
            if (count >= partLen)
            {
                Buffer.BlockCopy(input, offset, this._buffer, index, partLen);
                Transform(this._buffer, 0);

                for (i = partLen; i + 63 < count; i += 64)
                    Transform(input, offset + i);

                index = 0;
            }
            else
                i = 0;

            // Buffer remaining input 
            Buffer.BlockCopy(input, offset + i, this._buffer, index, count - i);
        }

        // MD5 finalization. Ends an MD5 message-digest operation, writing the the message digest and zeroizing the context.
        protected override byte[] HashFinal()
        {
            byte[] digest = new byte[16];
            byte[] bits = new byte[8];
            int index, padLen;

            // Save number of bits
            Encode(bits, 0, this._count, 0, 8);

            // Pad out to 56 mod 64.
            index = (int)((uint)(this._count[0] >> 3) & 0x3f);
            padLen = (index < 56) ? (56 - index) : (120 - index);
            HashCore(_padding, 0, padLen);

            // Append length (before padding)
            HashCore(bits, 0, 8);

            // Store state in digest 
            Encode(digest, 0, _state, 0, 16);

            // Zeroize sensitive information.
            _count[0] = _count[1] = 0;
            _state[0] = 0;
            _state[1] = 0;
            _state[2] = 0;
            _state[3] = 0;

            // initialize again, to be ready to use
            Initialize();

            return digest;
        }

        private const byte S11 = 7;
        private const byte S12 = 12;
        private const byte S13 = 17;
        private const byte S14 = 22;
        private const byte S21 = 5;
        private const byte S22 = 9;
        private const byte S23 = 14;
        private const byte S24 = 20;
        private const byte S31 = 4;
        private const byte S32 = 11;
        private const byte S33 = 16;
        private const byte S34 = 23;
        private const byte S41 = 6;
        private const byte S42 = 10;
        private const byte S43 = 15;
        private const byte S44 = 21;

        // MD5 basic transformation. Transforms state based on 64 bytes block.
        private void Transform(byte[] block, int offset)
        {
            uint a = _state[0], b = _state[1], c = _state[2], d = _state[3];
            uint[] x = new uint[16];
            Decode(x, 0, block, offset, 64);

            // Round 1
            FF(ref a, b, c, d, x[0], S11, 0xd76aa478); /* 1 */
            FF(ref d, a, b, c, x[1], S12, 0xe8c7b756); /* 2 */
            FF(ref c, d, a, b, x[2], S13, 0x242070db); /* 3 */
            FF(ref b, c, d, a, x[3], S14, 0xc1bdceee); /* 4 */
            FF(ref a, b, c, d, x[4], S11, 0xf57c0faf); /* 5 */
            FF(ref d, a, b, c, x[5], S12, 0x4787c62a); /* 6 */
            FF(ref c, d, a, b, x[6], S13, 0xa8304613); /* 7 */
            FF(ref b, c, d, a, x[7], S14, 0xfd469501); /* 8 */
            FF(ref a, b, c, d, x[8], S11, 0x698098d8); /* 9 */
            FF(ref d, a, b, c, x[9], S12, 0x8b44f7af); /* 10 */
            FF(ref c, d, a, b, x[10], S13, 0xffff5bb1); /* 11 */
            FF(ref b, c, d, a, x[11], S14, 0x895cd7be); /* 12 */
            FF(ref a, b, c, d, x[12], S11, 0x6b901122); /* 13 */
            FF(ref d, a, b, c, x[13], S12, 0xfd987193); /* 14 */
            FF(ref c, d, a, b, x[14], S13, 0xa679438e); /* 15 */
            FF(ref b, c, d, a, x[15], S14, 0x49b40821); /* 16 */

            // Round 2
            GG(ref a, b, c, d, x[1], S21, 0xf61e2562); /* 17 */
            GG(ref d, a, b, c, x[6], S22, 0xc040b340); /* 18 */
            GG(ref c, d, a, b, x[11], S23, 0x265e5a51); /* 19 */
            GG(ref b, c, d, a, x[0], S24, 0xe9b6c7aa); /* 20 */
            GG(ref a, b, c, d, x[5], S21, 0xd62f105d); /* 21 */
            GG(ref d, a, b, c, x[10], S22, 0x2441453); /* 22 */
            GG(ref c, d, a, b, x[15], S23, 0xd8a1e681); /* 23 */
            GG(ref b, c, d, a, x[4], S24, 0xe7d3fbc8); /* 24 */
            GG(ref a, b, c, d, x[9], S21, 0x21e1cde6); /* 25 */
            GG(ref d, a, b, c, x[14], S22, 0xc33707d6); /* 26 */
            GG(ref c, d, a, b, x[3], S23, 0xf4d50d87); /* 27 */
            GG(ref b, c, d, a, x[8], S24, 0x455a14ed); /* 28 */
            GG(ref a, b, c, d, x[13], S21, 0xa9e3e905); /* 29 */
            GG(ref d, a, b, c, x[2], S22, 0xfcefa3f8); /* 30 */
            GG(ref c, d, a, b, x[7], S23, 0x676f02d9); /* 31 */
            GG(ref b, c, d, a, x[12], S24, 0x8d2a4c8a); /* 32 */

            // Round 3
            HH(ref a, b, c, d, x[5], S31, 0xfffa3942); /* 33 */
            HH(ref d, a, b, c, x[8], S32, 0x8771f681); /* 34 */
            HH(ref c, d, a, b, x[11], S33, 0x6d9d6122); /* 35 */
            HH(ref b, c, d, a, x[14], S34, 0xfde5380c); /* 36 */
            HH(ref a, b, c, d, x[1], S31, 0xa4beea44); /* 37 */
            HH(ref d, a, b, c, x[4], S32, 0x4bdecfa9); /* 38 */
            HH(ref c, d, a, b, x[7], S33, 0xf6bb4b60); /* 39 */
            HH(ref b, c, d, a, x[10], S34, 0xbebfbc70); /* 40 */
            HH(ref a, b, c, d, x[13], S31, 0x289b7ec6); /* 41 */
            HH(ref d, a, b, c, x[0], S32, 0xeaa127fa); /* 42 */
            HH(ref c, d, a, b, x[3], S33, 0xd4ef3085); /* 43 */
            HH(ref b, c, d, a, x[6], S34, 0x4881d05); /* 44 */
            HH(ref a, b, c, d, x[9], S31, 0xd9d4d039); /* 45 */
            HH(ref d, a, b, c, x[12], S32, 0xe6db99e5); /* 46 */
            HH(ref c, d, a, b, x[15], S33, 0x1fa27cf8); /* 47 */
            HH(ref b, c, d, a, x[2], S34, 0xc4ac5665); /* 48 */

            // Round 4
            II(ref a, b, c, d, x[0], S41, 0xf4292244); /* 49 */
            II(ref d, a, b, c, x[7], S42, 0x432aff97); /* 50 */
            II(ref c, d, a, b, x[14], S43, 0xab9423a7); /* 51 */
            II(ref b, c, d, a, x[5], S44, 0xfc93a039); /* 52 */
            II(ref a, b, c, d, x[12], S41, 0x655b59c3); /* 53 */
            II(ref d, a, b, c, x[3], S42, 0x8f0ccc92); /* 54 */
            II(ref c, d, a, b, x[10], S43, 0xffeff47d); /* 55 */
            II(ref b, c, d, a, x[1], S44, 0x85845dd1); /* 56 */
            II(ref a, b, c, d, x[8], S41, 0x6fa87e4f); /* 57 */
            II(ref d, a, b, c, x[15], S42, 0xfe2ce6e0); /* 58 */
            II(ref c, d, a, b, x[6], S43, 0xa3014314); /* 59 */
            II(ref b, c, d, a, x[13], S44, 0x4e0811a1); /* 60 */
            II(ref a, b, c, d, x[4], S41, 0xf7537e82); /* 61 */
            II(ref d, a, b, c, x[11], S42, 0xbd3af235); /* 62 */
            II(ref c, d, a, b, x[2], S43, 0x2ad7d2bb); /* 63 */
            II(ref b, c, d, a, x[9], S44, 0xeb86d391); /* 64 */

            _state[0] += a;
            _state[1] += b;
            _state[2] += c;
            _state[3] += d;

            // Zeroize sensitive information.
            for (int i = 0; i < x.Length; i++)
                x[i] = 0;
        }

        // Encodes input (uint) into output (byte). Assumes len is multiple of 4.
        private static void Encode(byte[] output, int outputOffset, uint[] input, int inputOffset, int count)
        {
            int i, j;
            int end = outputOffset + count;
            for (i = inputOffset, j = outputOffset; j < end; i++, j += 4)
            {
                output[j] = (byte)(input[i] & 0xff);
                output[j + 1] = (byte)((input[i] >> 8) & 0xff);
                output[j + 2] = (byte)((input[i] >> 16) & 0xff);
                output[j + 3] = (byte)((input[i] >> 24) & 0xff);
            }
        }

        // Decodes input (byte) into output (uint). Assumes len is a multiple of 4.
        static private void Decode(uint[] output, int outputOffset, byte[] input, int inputOffset, int count)
        {
            int i, j;
            int end = inputOffset + count;
            for (i = outputOffset, j = inputOffset; j < end; i++, j += 4)
                output[i] = ((uint)input[j]) | (((uint)input[j + 1]) << 8) | (((uint)input[j + 2]) << 16) | (((uint)input[j + 3]) << 24);
        }
    }

}
